src/hotspot/share/gc/shared/cardTableBarrierSet.cpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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#include "precompiled.hpp"
#include "gc/shared/cardTableBarrierSetAssembler.hpp"
#include "gc/shared/cardTableBarrierSet.inline.hpp"
#include "gc/shared/collectedHeap.hpp"
#include "gc/shared/space.inline.hpp"
#include "logging/log.hpp"
#include "memory/virtualspace.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/thread.hpp"
#include "services/memTracker.hpp"
#include "utilities/align.hpp"
#include "utilities/macros.hpp"
#ifdef COMPILER1
#include "gc/shared/c1/cardTableBarrierSetC1.hpp"
#endif
#ifdef COMPILER2
#include "gc/shared/c2/cardTableBarrierSetC2.hpp"
#endif

class CardTableBarrierSetC1;
class CardTableBarrierSetC2;

// This kind of "BarrierSet" allows a "CollectedHeap" to detect and
// enumerate ref fields that have been modified (since the last
// enumeration.)

CardTableBarrierSet::CardTableBarrierSet(BarrierSetAssembler* barrier_set_assembler,
                                         BarrierSetC1* barrier_set_c1,
                                         BarrierSetC2* barrier_set_c2,
                                         CardTable* card_table,
                                         const BarrierSet::FakeRtti& fake_rtti) :
  ModRefBarrierSet(barrier_set_assembler,
                   barrier_set_c1,
                   barrier_set_c2,
                   fake_rtti.add_tag(BarrierSet::CardTableBarrierSet)),
  _defer_initial_card_mark(false),
  _card_table(card_table)
{}

CardTableBarrierSet::CardTableBarrierSet(CardTable* card_table) :
  ModRefBarrierSet(make_barrier_set_assembler<CardTableBarrierSetAssembler>(),
                   make_barrier_set_c1<CardTableBarrierSetC1>(),
                   make_barrier_set_c2<CardTableBarrierSetC2>(),
                   BarrierSet::FakeRtti(BarrierSet::CardTableBarrierSet)),
  _defer_initial_card_mark(false),
  _card_table(card_table)
{}

void CardTableBarrierSet::initialize() {
  initialize_deferred_card_mark_barriers();
}

CardTableBarrierSet::~CardTableBarrierSet() {
  delete _card_table;
}

void CardTableBarrierSet::write_ref_array_work(MemRegion mr) {
  if (_card_table->scanned_concurrently()) {
    // The array stores must not be reordered with the card marks if the
    // card table is scanned concurrently.
    OrderAccess::storestore();
  }
  _card_table->dirty_MemRegion(mr);
}

void CardTableBarrierSet::invalidate(MemRegion mr) {
  _card_table->invalidate(mr);
}

void CardTableBarrierSet::print_on(outputStream* st) const {
  _card_table->print_on(st);
}

// Helper for ReduceInitialCardMarks. For performance,
// compiled code may elide card-marks for initializing stores
// to a newly allocated object along the fast-path. We
// compensate for such elided card-marks as follows:
// (a) Generational, non-concurrent collectors, such as
//     GenCollectedHeap(ParNew,DefNew,Tenured) and
//     ParallelScavengeHeap(ParallelGC, ParallelOldGC)
//     need the card-mark if and only if the region is
//     in the old gen, and do not care if the card-mark
//     succeeds or precedes the initializing stores themselves,
//     so long as the card-mark is completed before the next
//     scavenge. For all these cases, we can do a card mark
//     at the point at which we do a slow path allocation
//     in the old gen, i.e. in this call.
// (b) GenCollectedHeap(ConcurrentMarkSweepGeneration) requires
//     in addition that the card-mark for an old gen allocated
//     object strictly follow any associated initializing stores.
//     In these cases, the memRegion remembered below is
//     used to card-mark the entire region either just before the next
//     slow-path allocation by this thread or just before the next scavenge or
//     CMS-associated safepoint, whichever of these events happens first.
//     (The implicit assumption is that the object has been fully
//     initialized by this point, a fact that we assert when doing the
//     card-mark.)
// (c) G1CollectedHeap(G1) uses two kinds of write barriers. When a
//     G1 concurrent marking is in progress an SATB (pre-write-)barrier
//     is used to remember the pre-value of any store. Initializing
//     stores will not need this barrier, so we need not worry about
//     compensating for the missing pre-barrier here. Turning now
//     to the post-barrier, we note that G1 needs a RS update barrier
//     which simply enqueues a (sequence of) dirty cards which may
//     optionally be refined by the concurrent update threads. Note
//     that this barrier need only be applied to a non-young write,
//     but, like in CMS, because of the presence of concurrent refinement
//     (much like CMS' precleaning), must strictly follow the oop-store.
//     Thus, using the same protocol for maintaining the intended
//     invariants turns out, serendepitously, to be the same for both
//     G1 and CMS.
//
// For any future collector, this code should be reexamined with
// that specific collector in mind, and the documentation above suitably
// extended and updated.
void CardTableBarrierSet::on_slowpath_allocation_exit(JavaThread* thread, oop new_obj) {
#if COMPILER2_OR_JVMCI
  if (!ReduceInitialCardMarks) {
    return;
  }
  // If a previous card-mark was deferred, flush it now.
  flush_deferred_card_mark_barrier(thread);
  if (new_obj->is_typeArray() || _card_table->is_in_young(new_obj)) {
    // Arrays of non-references don't need a post-barrier.
    // The deferred_card_mark region should be empty
    // following the flush above.
    assert(thread->deferred_card_mark().is_empty(), "Error");
  } else {
    MemRegion mr((HeapWord*)new_obj, new_obj->size());
    assert(!mr.is_empty(), "Error");
    if (_defer_initial_card_mark) {
      // Defer the card mark
      thread->set_deferred_card_mark(mr);
    } else {
      // Do the card mark
      invalidate(mr);
    }
  }
#endif // COMPILER2_OR_JVMCI
}

void CardTableBarrierSet::initialize_deferred_card_mark_barriers() {
  // Used for ReduceInitialCardMarks (when COMPILER2 or JVMCI is used);
  // otherwise remains unused.
#if COMPILER2_OR_JVMCI
  _defer_initial_card_mark = is_server_compilation_mode_vm() && ReduceInitialCardMarks
                             && (DeferInitialCardMark || card_mark_must_follow_store());
#else
  assert(_defer_initial_card_mark == false, "Who would set it?");
#endif
}

void CardTableBarrierSet::flush_deferred_card_mark_barrier(JavaThread* thread) {
#if COMPILER2_OR_JVMCI
  MemRegion deferred = thread->deferred_card_mark();
  if (!deferred.is_empty()) {
    assert(_defer_initial_card_mark, "Otherwise should be empty");
    {
      // Verify that the storage points to a parsable object in heap
      DEBUG_ONLY(oop old_obj = oop(deferred.start());)
      assert(!_card_table->is_in_young(old_obj),
             "Else should have been filtered in on_slowpath_allocation_exit()");
      assert(oopDesc::is_oop(old_obj, true), "Not an oop");
      assert(deferred.word_size() == (size_t)(old_obj->size()),
             "Mismatch: multiple objects?");
    }
    write_region(deferred);
    // "Clear" the deferred_card_mark field
    thread->set_deferred_card_mark(MemRegion());
  }
  assert(thread->deferred_card_mark().is_empty(), "invariant");
#else
  assert(!_defer_initial_card_mark, "Should be false");
  assert(thread->deferred_card_mark().is_empty(), "Should be empty");
#endif
}

void CardTableBarrierSet::on_thread_detach(JavaThread* thread) {
  // The deferred store barriers must all have been flushed to the
  // card-table (or other remembered set structure) before GC starts
  // processing the card-table (or other remembered set).
  flush_deferred_card_mark_barrier(thread);
}

bool CardTableBarrierSet::card_mark_must_follow_store() const {
 return _card_table->scanned_concurrently();
}